1. Field of the Invention
This invention relates in general to hydraulic power steering pumps of the balanced vane type for use in automotive or mobile equipment applications, and in particular to hydraulic, power steering pumps having balanced low-pressure porting and a pressure plate.
2. Description of Related Art
Conventional balanced vane hydraulic pumps used in power steering applications have a generally cylindrical steel rotor with multiple vanes rotating within an oval path that is machined into a powdered iron cam ring. This mechanical arrangement is shown in simplified form in FIG. 1, where the rotor 20 has ten vanes 21-30 which rotate under power provided through a splined drive shaft 31. The outer edges of the vanes 21-30 are generally beveled or otherwise sharpened to a straight edge, and follow the generally elliptical machined inner surface 32 of cam ring 34 which is held in place relative to the pump housing (not shown in FIG. 1) by locator pins 36 and 38. The outer shape 40 of cam ring 34 is normally cylindrical. The high pressure outlet ports or "windows" 42 and 44 are shown in dashed lines at the top and bottom of the cam ring diametrically opposite to one another. The direction of pressure outlet ports or "windows" 42 and 44 are shown in dashed lines at the top and bottom of the cam ring diametrically opposite to one another. The direction of rotor rotation is Clockwise as indicated by arrow 45 in FIG. 1. The inlet ports or windows 46 and 48 are shown in dashed and solid lines and are diametrically opposite to one another, on the left side and right side respectively of cam ring 34.
In a conventional balanced vane pump, each vane is pressed outwardly against the inner surface 32 of the cam ring 34 by centrifugal force, and slides in and out within its own radially-aligned slot in rotor 20, as it spins around the cam ring. Hydraulic assist is provided via high pressure hydraulic fluid ported to undervane holes 51-60 in the rotor, which are respectively associated with vanes 21-30, and are part of the undervane porting system, to help ensure that the vanes faithfully track the inner surface 32 of the cam ring 34.
FIG. 2 is a hydraulic diagram showing the fluid circuit coupling the two sets of diametrically-opposed ports or windows. Outlet ports 42 and 44 are respectively connected by conduits 62 and 64 to a common high pressure gallery 65. Inlet ports 46 and 48 are connected by conduits 66 and 68 to a common low pressure gallery 69. High pressure hydraulic fluid discharged from ports 42 and 44 flows as indicated by broad arrows 72 and 74 into one stream of fluid indicated by arrow 75 to a pressure relief and flow control valve (not shown in FIGS. 1 or 2) which is normally built into the pump housing. Low pressure fluid discharged from the relief valve or obtained from a hydraulic reservoir which is indicated by arrow 79, is divided into two flows indicated by arrow 76 and 78 and passed to the inlet ports 46 and 48.
The two discharge ports 42 and 44 are 180.degree. apart, as are the two inlet ports 46 and 48. Thus, pressures radially applied against the generally circular outer edge 80 of rotor 20 cancel each other. In this manner, forces on the rotor are largely balanced in a radial direction. Since two sets of ports are used, balanced vane pumps indicated by arrows 82 and 84 have two discharge or pumping quadrants or sectors 82 and 84, which discharge oil into outlet ports 42 and 44 respectively, and have two inlet quadrants or sectors, indicated by arrows 86 and 88, which respectively draw in fluid through inlet ports 46 and 48.
The displacement of a balanced vane pump, that is, its volumetric output per revolution, is fixed and depends on the width of the cam ring (which is the same as the width of the rotor), and the throw of the cam ring. Balanced vane pumps provide large displacements in a relatively small size package, especially since this type of pump can be operated at high speeds. Vane pumps are popular because of their small size, good efficiency, durability, capacity and speed ranges. Balanced vane pumps produce output pulsations that are low in amplitude, with a frequency corresponding to the number of vanes times the revolutions per second of the pump shaft. Conventional vane pumps are fairly quiet, but are known to whine at high speed.
Power steering pumps of the balanced vane type used in the automotive industry and mobile equipment industry typically include a pump cartridge sandwiched between a pressure plate in the cover of the pump housing and a thrust plate in the body of the pump housing. The pump cartridge consists of these two plates, the cam ring, rotor, and vanes. Internal porting is provided in the pump which allows the high pressure hydraulic flow created by the pump as ft operates to bear against the pressure plate. The pressure plate in turn bears against the cam ring in order to control clearances as pressure output increases. Specifically, this provides hydraulic squeeze which maintains or even reduces the operating clearance provided between the cam ring, rotor and vanes on the one hand and the thrust plate or pressure plate on the other hand as the hydraulic pressure increases. In this manner, pump efficiency and pressures obtainable are increased since significant leakage from one pumping chamber to the next which otherwise would occur is prevented. However, the use of the pressure and thrust plate concept increases the costs of manufacturing a power steering pump since these parts must be machined and assembled.
For the last fifteen years or so within the automobile industry, there has been an intense desire to reduce weight and manufacturing costs while maintaining or improving upon car performance. It is the primary object of the invention described in the co-pending application to provide a simplified balanced vane power steering pump which satisfies these goals. In particular, primary objectives of that invention included the following:
(1) to reduce the weight of the power steering pump by making the pump from fewer parts, and by making sections of the housing from lightweight metal castings or other lightweight materials; PA1 (2) to reduce manufacturing costs of the power steering pump by eliminating some of the machining operations required to make the housing and cover of a conventional power steering pump; and PA1 (3) to reduce the noise levels produced by the power steering pump, particularly at high speeds where conventional pumps are known to whine, by using a radially and axially balanced low pressure and high pressure porting systems. PA1 (1) to provide a power steering pump with reduced cavitation at high speeds by reducing turbulence through the use of a sculpted pressure plate; and PA1 (2) to provide a power steering pump that utilizes a pressure plate and/or a thrust plate for improved pumping efficiency by providing balanced low pressure flow and smooth transition porting on both sides of each of the two low pressure regions within the pump.
Still other objectives of the invention in the co-pending application are to provide a power steering pump with reduced cavitation at high speeds by reducing turbulence through the use of contoured and generally symmetrical galleries and passages to deliver low-pressure hydraulic fluid to four inlet windows.
The primary objective of the invention described in this application includes the following: